Watch out for these 10 most contaminated beaches in N.J.

It's a sunny day at the Jersey Shore, a perfect laze-in-the-sand scorcher.

Except there's one problem: Your favorite beach is closed.

Take heart, because it's almost certainly for good reason.

High bacteria levels from pollution and storm runoff close beaches up and down the coastline every summer, usually after storms with heavy rainfall, state data shows.

From 2005 to 2017, state officials closed beaches 212 times and issued 395 advisories for elevated bacteria levels, according to the data, compiled by the state Department of Environmental Protection. There were 28 closures in 2017 alone.

All that's an improvement from the 1980s and '90s when the muck on the beach was far more visible and disturbing: medical syringes and illegal dumping, which led to an "environmental catastrophe," said Cindy Zipf, executive director of Clean Ocean Action, an environmental group.

Hundreds of beach closures ensued every summer, Zipf said.

Pollution remains a stubborn problem, however, and it's a little harder to detect these days because it's not so visible. And the number of closures only tells a slice of the story. Consider:

The state can take days to close a beach, it only takes samples on Monday mornings in the summer, and only from beaches that have a lifeguard.

If results from a first test come back positive, it issues an advisory and takes another sample. If that comes back positive, the state closes the beach.

Still, Zipf said the program was a boon to beachgoers who can now make an informed choice before they swim.

"Knowledge is power," she said. "We just need to do more."

A note about the data: The names of the beaches were provided by the state Department of Environmental Protection and, in some cases, approximate a location based on a nearby street. They may be known locally by another name. Pre-emptive beach closings that were not based on testing were not included.

10. L Street Beach in Belmar

L Street Beach in Belmar Borough had 8 closures and 3 contamination advisories from 2005 to 2017, and all but one were for elevated bacterial levels. The exception was for a chemical oil spill.

8. Summit (tie) in Island Heights

Summit in Island Heights Borough had 2 closures and 10 contamination advisories from 2005 to 2017, all for elevated bacterial levels.

8. Brown Avenue South (tie) in Spring Lake

Brown Avenue South in Spring Lake Borough had 7 closures and 5 contamination advisories from 2005 to 2017, all for elevated bacterial levels.

7. Hancock in Seaside Heights

Hancock in Seaside Heights Borough had 6 closures and 7 contamination advisories from 2005 to 2017, all for elevated bacterial levels.